An electroluminescent (EL) device is characterized in that it emits light when an electrical voltage is applied and current flows. Such devices have long been known in engineering as xe2x80x9clight-emitting diodesxe2x80x9d (LEDs). The emission of light is due to the fact that positive charges (xe2x80x9cholesxe2x80x9d) and negative charges (xe2x80x9celectronsxe2x80x9d) recombine with the emission of light.
In the development of light-emitting components for electronics or photonics, use is mainly made at present of inorganic semiconductors, such as gallium arsenide. Punctiform indicating elements can be produced on the basis of such substances. Large-area devices are not possible.
In addition to semiconductor light-emitting diodes, electroluminescent devices based on vapour-deposited low-molecular-weight organic compounds are known U.S. Pat. No. 4,539,507, U.S. Pat. No. 4,769,262, U.S. Pat. No. 5,077,142, EP-A 406 762, EP-A 278 758, EP-A 278 757).
Furthermore, polymers, such as poly(p-phenylenes) and poly(p-phenylenevinylenes) (PPV) are described as electroluminescent polymers: G. Leising et al., Adv. Mater. 4 (1992) No. 1; Friend et al., J Chem. Soc., Chem. Commun. 32 (1992); Saito et al., Polymer, 1990, Vol. 31, 1137; Friend et al., Physical Review B, Vol. 42, No. 18, 11670 or WO 90/13148. Further examples of PPV in electroluminescent indicators are described in EP-A 443 861, WO-A-9203490 and 92003491.
EP-A 0 294 061 discloses an optical modulator based on polyacetylene.
Heeger et al. have proposed soluble, conjugated PPV derivatives for producing flexible polymeric LEDs (WO 92/16023). Polymer blends of various compositions are likewise known: M. Stolka et al., Pure and Appl. Chem., Vol. 67, No. 1, pp 175-182, 1995; H. Bxc3xa4ssler et al., Adv. Mater. 1995, 7, No. 6, 551; K. Nagai et al., Appl. Phys. Lett. 67 (16), 1995, 2281; EP-A 532 798.
As a rule, the organic EL devices contain one or more layers of organic charge transport compounds. The basic structure of the layer sequence is as follows:
1 Carrier, substrate
2 Base electrode
3 Hole-injecting layer
4 Hole-transporting layer
5 Light-emitting layer
6 Electron-transporting layer
7 Electron-injecting layer
8 Top electrode
9 Contacts
10 Packaging, encapsulation.
The layers 3 to 7 are the electroluminescent element.
This structure is the most general case and can be simplified by omitting individual layers so that one layer assumes a plurality of tasks. In the simplest case, an EL device comprises two electrodes between which an organic layer is situated which fulfils all the functions, including the emission of light. Such systems are described, for example, in Application WO 90/13148 on the basis of poly(p-phenylenevinylene).
Multilayer systems can be constructed by vapour-deposition processes in which the layers are applied successively from the gas phase or by pouring methods. Because of the higher processing speed, pouring methods are preferred. However, in certain cases, the process of partially dissolving a layer already applied may present a difficulty in depositing the next layer on top.
The object of the present invention is to provide electroluminescent devices having high luminous density, the mixture to be applied being pourable, i.e. capable of being applied from solution.
It was found that electroluminescent devices containing material A or a blend of material A with polymeric binder B, mentioned below fulfil these requirements. In the following, the term zone is also to be equated with layer.
The present invention therefore relates to electroluminescent devices containing, as electroluminescent material A, at least one oligomer of substituted p-divinylbenzene having the general formula (I) 
in which
R1 and R2 independently represent hydrogen, or linear alkyl or alkoxy containing 1 to 12 carbon atoms, preferably 1 to 8 carbon atoms, or branched alkyl or alkoxy containing 3 to 12, preferably 3 to 8 carbon atoms, or cycloalkyl containing 4 to 10, preferably 5 or 6 carbon atoms, with the proviso that
R1 and R2 may not both by hydrogen,
R3 and R4 are identical or different and represent hydrogen, C1-C6-alkyl (preferably methyl or ethyl), CN or halogen (preferably fluorine, chlorine or bromine),
R5, R6 R7 and R8 are identical or different and may be any desired radicals, inter alia, radicals suitable for coupling oligomers to other oligomers/polymers,
n is an integer from 2 to 20, preferably 2 to 15 and particularly preferably 2 to 10,
R5 and R7 represent independently of one another, preferably hydrogen or alkyl, in particular C1-C4-alkyl, very particularly preferably methyl,
R6 and R8 represent, independently of one another, preferably alkyl or aryl radical, in particular C1-C6-alkyl or phenyl. The alkyl and phenyl radicals may contain one or more functional groups, such as, for example, xe2x80x94OH, xe2x80x94CN, xe2x80x94CHO or Br.
With suitable substitution, the oligomers of substituted divinylbenzene may also be incorporated, for example, in polymers as discussed below, by means of functional groups. In this connection, it is possible to produce both main-chain and side-chain polymers containing low-molecular-weight compounds.
The oligomers may be coupled to polymers containing double bonds, for example unsaturated polymers, such as polybutadiene and polyoctamer by metathetic incorporation (cross-metathesis reaction of the oligomers and an unsaturated polymer).
The electroluminescent device is made up of an anode, an electroluminescent element and a cathode, at least one of the two electrodes being transparent or semi transparent in the visible spectral range. The electroluminescent element contains:
A hole-injecting zone, a hole-transporting zone, an electroluminescent zone, an electron-transporting zone and/or an electron-injecting zone, characterized in that the electroluminescent element optionally contains a functionalized compound from the group comprising the hole-transporting materials, a luminescent material A and, optionally, electron-transporting materials, at least one zone being present, individual zones being omitted and the joined zone(s) taking over a multiplicity of tasks.
A zone can take over a multiplicity of tasks, i.e., a zone may contain, for example, hole-injecting, hole-transporting, electroluminescent, electron-injecting and/or electron-transporting substances.
The electroluminescent element may furthermore contain one or more transparent polymeric binders B.
An additional embodiment of the invention relates to the device comprising the product of reaction of the oligomer of formula (I) and a polymeric resin containing double bonds, for example unsaturated polymers, such as polybutadiene or polyoctamer.
The oligomers of substituted p-divinylbenzene may be produced by known methods, for example by metathesis reactions, which are described in Macromol. Rapid Commun., 16 (1995), 149 (cf. also Examples).
The products are soluble in common solvents. They can be processed to form transparent films which, depending on the value of n and/or the choice of substituents on the phenyl ring, exhibit different photoluminescents. By varying n and/or the choice of the substituents, the wavelength (color) of the emitted light can therefore be systematically adjusted.
The binder B represents polymers and/or copolymers, such as, for example, polycarbonates, polyester carbonates, copolymers of styrenes, such as SAN or styrene acrylates, polysulfones, polymers based on vinyl-group-containing monomers, such as, for example, poly(meth)acrylates, polyvinylpyrrolidone, polyvinylcarbazole, vinyl-acetate and vinyl-alcohol polymers and copolymers, polyolefins, cyclic olefin copolymers, phenoxy resins, etc. Mixtures of different polymers can also be used. The polymeric binders B have molecular weights of from 10,000 to 200,000 g/mol., are soluble and film-forming and are transparent in the visible spectral range. They are described, for example, in Encyclopedia of Polymer Science and Engineering, 2nd ed., A. Wiley-Interscience Publication. The electroluminescent material A may be dispersed in the transparent binders B. The concentration ratios are variable as desired. Binder B is normally used in an amount of up to 95, preferably up to 80%, based on the total weight of A and B.
To produce the layer, the components A) and, optionally, B) are dissolved in a suitable solvent, such as chloroform and are applied to a suitable substrate by pouring, doctor-blading or spin-coating. Suitable substrates include glass or a plastics material which is provided with a transparent electrode. A sheet of polycarbonate, polyester, such as polyethylene terephthalate or polyethylene naphthalate, polysulfone or polyimide may be used as plastics material.
Suitable as transparent or semi transparent electrodes are:
a) metal oxides, for example indium/tin oxide (ITO), tin oxide (NESA) zinc oxide, doped tin oxide, doped zinc oxide, etc.,
b) semi-transparent metal films, for example, Au, Pt, Ag, Cu, etc.,
c) conductive polymer films, such as polyanilines, polythiophenes, etc.
The metal oxide film electrodes and the semi-transparent metal-film electrodes are applied by procedures such as vapor deposition, sputtering, platinum, coating, etc., in thin layer. The conductive polymer films are applied by procedures such as spin-coating, casting, doctor-blading, etc., from solution.
The thickness of the electrode is at least 3 nanometers (nm), preferably 10 nm to 500 nm.
The electroluminescent layer is applied directly as a thin film to the electrode or to an optionally present charge-transporting layer. The thicknesses of the film is 10 to 500 nm, preferably 20 to 400 nm, particularly preferably 50 to 250 nm.
A further charge-transporting layer may be inserted on the electroluminescent layer before a counterelectrode is applied.
An assembly of suitable charge-transporting interlayers which may be hole-conducting and/or electron-conducting materials which may be present in polymeric or low-molecular-weight form, optionally as a blend, is disclosed in EP-A 532 798, incorporated herein by reference. Particularly suitable are specially substituted polythiophene which have hole-transporting properties. They are described, for example, in EP-A 686 662 incorporated herein by reference.
The content of low-molecular-weight hole conductor in a polymer binder can be varied in the range from 2 to 97%; preferably, 5 to 95%, particularly preferably 10 to 90% , in particular 10 to 85% relative to the weight of the polymeric binder and hole conductor. The hole-injecting or hole-conducting zones can be deposited by various methods.
Film-forming hole conductors can also be used in pure form (100%). Optionally, the hole-injecting or hole-conducting zone may also contain proportions of an electroluminescent substance.
Blends which are composed exclusively of oligomers of substituted divinylbenzene may be vapor-deposited; soluble and film-forming blends, which may also contain (not necessarily) a binder B) in addition to low-molecular-weight compounds, may be deposited from a solution, for example, by means of spin-coating, pouring or doctor-blading.
It is also possible to apply emitting and/or electron-conducting substances in a separate layer to the hole-conducting layer containing the component A. In this connection, an emitting substance may also be added (as xe2x80x9cdopantxe2x80x9d) to the layer containing the compound A and an electron-conducting substance additionally applied. An electroluminescent substance may also be added to the electron-injecting or electron-conducting layer.
On the other hand, the electroluminescent materials A) may themselves also be used as dopants in electroluminescent devices.
The content of low-molecular-weight electron conductors in the polymeric binder can be varied in the range from 2 to 95%, preferably, 5 to 90%, particularly preferably 10 to 85% relative to the total weight of electron conductor and binder. Film-forming electron conductors may also be used in pure form (100%).
The counterelectrode is composed of a conductive substance, which may be transparent. Preferably, metals, for example Al, Au, Ag, Mg, In, etc. or alloys and oxides of the later which can be applied by procedures such as vapor deposition, sputtering or platinum coating, are suitable.
The device according to the invention is brought into contact with the two electrodes by two electrical leads (for example, metal wires).
When a direct voltage in the range from 0.1 to 100 volts is applied, the devices emit light of a wavelength from 200 to 2000 nm. They exhibit photoluminescence in the range from 200 to 2000 nm.
The devices according to the invention are suitable for producing units for the purpose of illumination and for the purpose of displaying information.
1. Metathetic preparation of ring-substitution p-phenylenevinylene oligomers (and polymers)
Starting from a 2,5-ring-substituted 1,4-(bis-1-alkenyl)benzene, such as, for example, 1,4-divinylbenzene, 1,4-di(1-propenyl)benzene, 1,4-di(1-isobutenyl)benzene etc. and adding a metathesis-active catalyst, such as, for example, Mo(NArMe2)(CHCMe2Ph)[OCMe(CF3)2]2, oligomerization (metathetic polycondensation) is carried out by cleaving and removing a low-molecular-weight monoolefin, such as, for example, ethene, 2-butene, 3-hexene, etc. Scheme 1 shows the reaction equation for the metathetic conversion of 2,5-disubstituted 1,4-divinylbenzenze.
Mo(NArMe2)(CHCMe2Ph)[OCMe(CF3)2]2: The synthesis is carried out according to the literature specification of R. R. Schrock, J. S. Murdzek, G. C. Bazan, J. Robbins, M. DiMare, M. O""Regan, J. Chem, Soc., 112 (1990), 3875. 
R1 and R2 independently are hydrogen, alkyl or alkoxy substituents, and n is 2 to 20.
The polycondensation reactions are carried out under an inert gas stream, argon being used, from which oxygen traces and water traces and water traces are removed ( less than 10xe2x88x925% by volume) by means of an xe2x80x9cOxisorbRxe2x80x9d miniature absorber (supplied by Messer-Griexcex2heim, Duisburg, Germany). A schlenk tube or a flask provided with inert gas and vacuum connections (standard Schlenk technique) is used as reaction vessel.
Before use, the glassware is baked out for approximately 4 hours under a mercury-diffusion-pump vacuum and then filled with argon.
The solvents toluene, decalin, cyclohexane, hexane, pentane are refluxed for 2 to 3 days over lithium alanate and distilled off under argon. 0.5 ml of n-butyllithium are then added to 250 ml of solvent, subjected to a plurality of freezing/thawing cycles until vacuum constancy is reached (mercury-diffusion-pump vacuum) and condensed over into a stock vessel.
The polycondensation of dibutyl-, diheptyl- or didecyl-substituted divinylbenzenes and the protection (cross metathesis) of the alkyl-substituted p-divinylbenzene oligomers are carried out at room temperature. The conversion of dicyclohexyl- or diheptyloxy-substituted p-divinylbenzenes is carried out at an elevated temperature of 50xc2x0 C. and up to 80xc2x0 C.